My family and I all spent hundreds of dollars on Okra Pepsin years ago, and it did zippo for all of us. Maybe this is because we are all fairly dedicated bowel cleansers, but still I expected at least something, and nothing happened at all.
I don't know about marshmallow, I haven't tried it, but there's lots of good info about it out there. I am thinking it might be cheaper and better to buy marshmallow as the lose herb rather than a tiny bottle of capsules, if you are going to be taking it for a while.
Anyway, I'd be very interested to hear your results if you try this.
One more thing! I cleaned my small intestine very effectively (as far as I can tell), with my last Dr Jenson style bowel cleanse. I removed lots of young-ish mucoid plaque, with identifiable striations from the jejunum, ileum and even the duodenum.